Vascular complications are a leading cause of mortality and morbidity in diabetic individuals. Despite recent advances using pharmacotherapy, a cure for diabetic microvascular complications (MVC) has yet to be realized. A conceptual and technical breakthrough is imperative to identify novel targets, and a strategy to cure these complications is paramount. We believe that our provocative preliminary data coupled with recent evidence of a potential role of endothelial progenitor cells (EPCs) in vascular repair and the discovery of the vasoprotective axis of the renin-angiotensin-system (RAS) offer such a breakthrough. The protective axis of the RAS involves the angiotensin converting enzyme 2 (ACE2) which is present in both endothelial cells and EPCs and generates angiotensin-(1-7) which acting through the Mas, attenuates the vasoconstrictive, proliferative, fibrotic and hypertrophic effects of angiotensin II, the key member of the deleterious axis of RAS. In this proposal we utilize retinopathy as the MVC to test our hypothesis that the ACE/ACE2 balance within EPCs dictates their reparative capability and can therefore predict progression of retinal MVC. If MVC are already present, then genetically modifying EPCs utilizing AAV technology to increase endogenous levels of ACE2 will enhance their reparative function and reverse MVC. We put forth the following Specific Aims to test our hypothesis: Aim 1: Investigate whether the ACE/ACE2 imbalance within EPCs will predict progression of MVC. Aim 2: Test the hypothesis if the absence of ACE2 in the systemic vasculature will accelerate progression while overexpression will prevent development and progression retinovascular complications. Aim 3: Investigate the hypothesis that increased ACE2/Ang-(1-7) expression within the retina will stimulate mobilization, homing and reparative potential of EPCs. This integrative and multidimensional proposal is extremely innovative both conceptually and technically because it will: (i) provide evidence for our hypothesis;(ii) establish the mechanism by which the activation of the ACE2/Ang-(1-7)-Mas receptor axis within EPCs sustains cellular reparative function in diabetes;(iii) determine whether the state of the RAS in EPCs can predict the progression of retinopathy;(iv) use the highly innovative VESsel GENeration (VESGEN) technology to delineate vascular remodeling in the retina and (iv) put us in an outstanding position to transition into the clinical arena using cells that have their protective RAS axis activated, either genetically or pharmacologically, for treatment of diabetic retinopathy PUBLIC HEALTH RELEVANCE: The focus of our proposal is to investigate if the balance of vasoprotective axis vs. vasodeleterious axis of the RAS within EPCs can predict progression of MVC in diabetes. Furthermore we will study if correction of this imbalance in the EPCs of diabetic patients would prevent the progression/attenuation of MVC. Outcome of these experiments will be a significant advancement in the use of ACE/ACE2 ratio as a predictor of diabetic patients and development of novel stem cell-based therapy to prevent MVC, single most important cause of diabetes-linked mortality and morbidity.